WASHINGTON (CNN) -- Reports of sexual assault among U.S. troops stationed in Iraq and Afghanistan rose 26 percent from the previous year, according to an annual Pentagon report presented to Congress on Tuesday.

Among all active duty U.S. military troops, the Pentagon showed an increase of about 8 percent in sexual assault reports from the previous year.

Dr. Kaye Whitley, director of the Pentagon's Sexual Assault Prevention and Response office, told reporters she attributes the increases to improved reporting methods and officials' belief that military personnel are less fearful of backlash from commanders and peers after reporting an assault.

"The increase in reports means the department's policy of encouraging victims to come forward is making a difference," Whitley said.

There were 165 sexual assault reports in Iraq and Afghanistan in fiscal year 2008, which began October 1, 2007. In fiscal year 2007, which began October 1, 2006, 131 sexual assaults were reported.

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For fiscal year 2008, there were 2,923 reports of sexual assaults among active duty U.S. troops worldwide, up from 2,688 reported the previous fiscal year.

There are 1.4 million active duty U.S. military stationed around the world.

Whitley said it is impossible to tell how much the number of actual sexual assaults may have risen.

"Just like the civilian communities, we have no way of knowing how many are occurring," she said.

The report defines sexual assault as unwanted touching, from groping to rape. The statistics are not comparable to the general U.S. population because the information gathered differs from civilian data, according to Pentagon officials.

Officials said the data is based on sexual assault reports involving at least one person with the active duty military, either as the alleged attacker or the alleged victim.

Pentagon officials said that even though there have been improvements that allow military personnel to report cases, they estimate that only between 10 percent and 20 percent of people who were sexually assaulted report the crime.

According to Tuesday's report, in fiscal year 2008 the Army said it fielded 1,584 reports. Of those, 1,328 alleged victims chose to report the full details while the rest opted to keep the information "restricted."

The Air Force reported a total of 607 cases, of which 387 were fully detailed. The Navy had a total of 489 reported cases, of which 348 were fully detailed. The Marines, the smallest branch of service, reported 243 sexual assault cases, with 216 fully detailed.

"While we don't want to pressure victims, we would like to see more people convert their reports [from restricted to unrestricted] or to report initially unrestricted so that we can hold all offenders accountable," Whitley said.

She said the services investigated 2,763 cases in fiscal year 2008 with 832 resulting in command action that included courts-martial, nonjudicial punishment or other administrative actions or discharges.

There were 317 courts-martial in fiscal year 2008 for sexual assaults in the military, which represents 38 percent of all command actions, an increase over the 30 percent in fiscal year 2007.